Wireless sensor including an RF signal circuit

ABSTRACT

A radio frequency identification (RFID) tag includes an antenna structure, a tank circuit, and a processing module that includes a tuning circuit. The processing module requires a processing module power level to operate according to a protocol. The tuning circuit requires a tuning circuit power level to adjust input impedance. The processing module power level is greater than the tuning circuit level. The processing module measures a first power level from a received RF signal. When the first power level is greater than the tuning circuit power level but less than the processing module power level, the processing module adjusts the input impedance to increase efficiency of power measurement and measures a second power level from the received RF signal. When and the second power level is greater than the processing module power level, the processing module uses the second power level to operate according to the protocol.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. § 120 as a continuation of U.S. Utility application Ser. No.15/272,907, entitled “WIRELESS SENSOR INCLUDING AN RF SIGNAL CIRCUIT”,filed Sep. 22, 2016, which claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/221,907, entitled “ActiveSelf-Calibrating RFID Sensors”, filed Sep. 22, 2015, which is herebyincorporated herein by reference in its entirety and made part of thepresent U.S. Utility patent application for all purposes.

U.S. Utility application Ser. No. 15/272,907 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 14/256,877, entitled “METHOD AND APPARATUS FORSENSING ENVIRONMENT USING A WIRELESS PASSIVE SENSOR”, filed Apr. 18,2014, now U.S. Pat. No. 9,785,807, issued on Oct. 10, 2017, which claimspriority pursuant to 35 U.S.C. § 119(e) to U.S. Provisional ApplicationNo. 61/814,241, entitled “RFID ENVIRONMENTAL SENSOR”, filed Apr. 20,2013; U.S. Provisional Application No. 61/833,150, entitled “RESONANTANTENNA”, filed Jun. 10, 2013; U.S. Provisional Application No.61/833,167, entitled “RFID TAG”, filed Jun. 10, 2013; U.S. ProvisionalApplication No. 61/833,265, entitled “RFID TAG”, filed Jun. 10, 2013;U.S. Provisional Application No. 61/871,167, entitled “RESONANTANTENNA”, filed Aug. 28, 2013; U.S. Provisional Application No.61/875,599, entitled “CMF ACCURATE SENSOR”, filed Sep. 9, 2013; U.S.Provisional Application No. 61/896,102, entitled “RESONANT ANTENNA”,filed Oct. 27, 2013; U.S. Provisional Application No. 61/929,017,entitled “RFID ENVIRONMENTAL SENSOR”, filed Jan. 18, 2014; U.S.Provisional Application No. 61/934,935, entitled “RFID ENVIRONMENTALSENSOR”, filed Feb. 3, 2014; all of which are hereby incorporated hereinby reference in their entirety and made part of the present U.S. Utilitypatent application for all purposes.

U.S. Utility application Ser. No. 14/256,877 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 13/209,420, entitled “METHOD AND APPARATUS FORDETECTING RF FIELD STRENGTH”, filed Aug. 14, 2011, now U.S. Pat. No.8,749,319, issued on Jun. 10, 2014, which claims priority pursuant to 35U.S.C. § 119(e) to U.S. Provisional Application No. 61/428,170, entitled“METHOD AND APPARATUS FOR VARYING AN IMPEDANCE”, filed Dec. 29, 2010 andU.S. Provisional Application No. 61/485,732, entitled “METHOD ANDAPPARATUS FOR SENSING ENVIRONMENTAL CONDITIONS USING AN RFID TAG”, filedMay 13, 2011, all of which are hereby incorporated herein by referencein their entirety and made part of the present U.S. Utility patentapplication for all purposes.

U.S. Utility application Ser. No. 13/209,420 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 12/462,331, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Aug. 1, 2009, now U.S. Pat. No. 8,081,043,issued on Dec. 20, 2011, which is a divisional of U.S. Utilityapplication Ser. No. 11/601,085, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Nov. 18, 2006, now U.S. Pat. No. 7,586,385,issued on Sep. 8, 2009, all of which are hereby incorporated herein byreference in their entirety and made part of the present U.S. Utilitypatent application for all purposes.

U.S. Utility application Ser. No. 14/256,877 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 13/209,425, entitled “METHOD AND APPARATUS FORDETECTING RF FIELD STRENGTH”, filed Aug. 14, 2011, now U.S. Pat. No.9,048,819, issued on Jun. 2, 2015, which claims priority pursuant to 35U.S.C. § 119(e) to U.S. Provisional Application No. 61/428,170, entitled“METHOD AND APPARATUS FOR VARYING AN IMPEDANCE”, filed Dec. 29, 2010 andU.S. Provisional Application No. 61/485,732, entitled “METHOD ANDAPPARATUS FOR SENSING ENVIRONMENTAL CONDITIONS USING AN RFID TAG”, filedMay 13, 2011, all of which are hereby incorporated herein by referencein their entirety and made part of the present U.S. Utility patentapplication for all purposes.

U.S. Utility application Ser. No. 13/209,425 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 12/462,331, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Aug. 1, 2009, now U.S. Pat. No. 8,081,043,issued on Dec. 20, 2011, which is a divisional of U.S. Utilityapplication Ser. No. 11/601,085, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Nov. 18, 2006, now U.S. Pat. No. 7,586,385,issued on Sep. 8, 2009, all of which are hereby incorporated herein byreference in their entirety and made part of the present U.S. Utilitypatent application for all purposes.

U.S. Utility application Ser. No. 14/256,877 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 13/467,925, entitled “ROLL-TO-ROLL PRODUCTION OFRFID TAGS”, filed May 9, 2012, which is a continuation-in-part of U.S.Utility application Ser. No. 13/209,425, entitled “METHOD AND APPARATUSFOR DETECTING RF FIELD STRENGTH”, filed Aug. 14, 2011, now U.S. Pat. No.9,048,819, issued on Jun. 2, 2015, which claims priority pursuant to 35U.S.C. § 119(e) to U.S. Provisional Application No. 61/428,170, entitled“METHOD AND APPARATUS FOR VARYING AN IMPEDANCE”, filed Dec. 29, 2010 andU.S. Provisional Application No. 61/485,732, entitled “METHOD ANDAPPARATUS FOR SENSING ENVIRONMENTAL CONDITIONS USING AN RFID TAG”, filedMay 13, 2011, all of which are hereby incorporated herein by referencein their entirety and made part of the present U.S. Utility patentapplication for all purposes.

U.S. Utility application Ser. No. 13/209,425 also claims prioritypursuant to 35 U.S.C. § 120 as a continuation-in-part of U.S. Utilityapplication Ser. No. 12/462,331, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Aug. 1, 2009, now U.S. Pat. No. 8,081,043,issued on Dec. 20, 2011, which is a divisional of U.S. Utilityapplication Ser. No. 11/601,085, entitled “METHOD AND APPARATUS FORVARYING AN IMPEDANCE”, filed Nov. 18, 2006, now U.S. Pat. No. 7,586,385,issued on Sep. 8, 2009, all of which are hereby incorporated herein byreference in their entirety and made part of the present U.S. Utilitypatent application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to wireless communications and moreparticularly to wireless sensors and applications thereof.

Description of Related Art

Wireless communication systems are known to include wirelesstransceivers that communication directly and/or over a wirelesscommunication infrastructure. In direct wireless communications, a firstwireless transceiver includes baseband processing circuitry and atransmitter to convert data into a wireless signal (e.g., radiofrequency (RF), infrared (IR), ultrasound, near field communication(NFC), etc.). Via the transmitter, the first wireless transceivertransmits the wireless signal. When a second wireless transceiver is inrange (e.g., is close enough to the first wireless transceiver toreceive the wireless signal at a sufficient power level), it receivesthe wireless signal via a receiver and converts the signal intomeaningful information (e.g., voice, data, video, audio, text, etc.) viabaseband processing circuitry. The second wireless transceiver maywirelessly communicate back to the first wireless transceiver in asimilar manner.

Examples of direct wireless communication (or point-to-pointcommunication) include walkie-talkies, Bluetooth, ZigBee, RadioFrequency Identification (RFID), etc. As a more specific example, whenthe direct wireless communication is in accordance with RFID, the firstwireless transceiver may be an RFID reader and the second wirelesstransceiver may be an RFID tag.

For wireless communication via a wireless communication infrastructure,a first wireless communication device transmits a wireless signal to abase station or access point, which conveys the signal to a wide areanetwork (WAN) and/or to a local area network (LAN). The signal traversesthe WAN and/or LAN to a second base station or access point that isconnected to a second wireless communication device. The second basestation or access point sends the signal to the second wirelesscommunication device. Examples of wireless communication via aninfrastructure include cellular telephone, IEEE 802.11, public safetysystems, etc.

In many situations, direct wireless communication is used to gatherinformation that is then communicated to a computer. For example, anRFID reader gathers information from RFID tags via direct wirelesscommunication. At some later point in time (or substantiallyconcurrently), the RFID reader downloads the gathered information to acomputer via a direct wireless communication or via a wirelesscommunication infrastructure.

In many RFID systems, the RFID tag is a passive component. As such, theRFID tag has to generate one or more supply voltages from the RF signalstransmitted by the RFID reader. Accordingly, a passive RFID tag includesa power supply circuit that converts the RF signal (e.g., a continuouswave AC signal) into a DC power supply voltage.

Once powered, the RFID tag receives a command from the RFID reader toperform a specific function. For example, if the RFID tag is attached toa particular item, the RFID tag stores a serial number, or some otheridentifier, for the item. In response to the command, the RFID tagretrieves the stored serial number and, using back-scattering, the RFIDtag transmits the retrieved serial number to the RFID reader.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a wirelesscommunication system in accordance with the present invention;

FIG. 2 is a schematic block diagram of an embodiment of a computingdevice in accordance with the present invention;

FIG. 3 is a schematic block diagram of an embodiment of a wirelesssensor in accordance with the present invention;

FIG. 4 is a schematic block diagram of another embodiment of a wirelesssensor in accordance with the present invention;

FIG. 5 is a schematic block diagram of an embodiment of a wireless datacollecting device and a wireless sensor in accordance with the presentinvention; and

FIG. 6 is a logic diagram of an embodiment of a method of sensing by awireless sensor in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a communicationsystem 10 that includes a plurality of sensor computing device 12, aplurality of user computing devices 14, a plurality of passive wirelesssensors 16-1 through 16-4, one or more wide area networks (WAN), and oneor more local area networks (LAN). The passive wireless sensors 16-1through 16-4, when activated, sense one or more of a variety ofconditions. For example, one passive wireless sensor senses for thepresence, absence, and/or amount of moisture in a given location (e.g.,in a room, in a manufactured item or component thereof (e.g., avehicle), in a bed, in a diaper, etc.). As another example, a passivewireless sensor senses pressure on and/or in a particular item (e.g., ona seat, on a bed, in a tire, etc.)

As yet another example, a passive wireless sensor senses temperaturewithin a space and/or of an item (e.g., surface temperature of the item,in a confined space such as a room or a box, etc.). As a furtherexample, a passive wireless sensor senses humidity within a space (e.g.,a room, a closet, a box, a container, etc.). As a still further example,a passive wireless sensor senses the presence and/or percentages of agas within a space (e.g., carbon monoxide in a car, carbon monoxide in aroom, gas within a food container, etc.). As an even further example, apassive wireless sensor senses the presence and/or percentages of alight within a space. As yet a further example, a passive wirelesssensor senses the presence, percentages, and/or properties of one ormore liquids in a solution. In one more example, a passive wirelesssensor senses location proximity of one item to another and/or theproximity of the passive wireless sensor to an item (e.g., proximity toa metal object, etc.).

In general, the sensor computing devices 12 function to collect thesensed data from the passive wireless sensors and process the senseddata. For example, a passive wireless sensor generates a coded valuerepresentative of a sensed condition (e.g., amount of moisture). Asensor computing device 12 receives the coded value and processes it todetermine an accurate measure of the sensed condition (e.g., a valuecorresponding to the amount of moisture such as 0% saturated, 50%saturated, 100% saturated, etc.).

The user computing devices 14 communication with one or more of thesensor computing devices 12 to gather the accurate measures of sensedconditions for further processing. For example, assume that the wirelesscommunication system is used by a manufacturing company that hasmultiple locations for assembly of its products. In particular, LAN 1 isat a first location where a first set of components of products areprocessed and the LAN 2 is at a second location where second componentsof the products and final assembly of the products occur. Further assumethat the corporate headquarters of the company is at a third location,where it communicates with the first and second locations via the WANand LANs.

In this example, the sensor computing device 12 coupled to LAN 1collects and processes data regarding the first set of components assensed by passive wireless sensors 16-1 and 16-2. The sensor computingdevice 12 is able to communicate this data to the user computing device14 coupled to the LAN 1 and/or to the computing device 14 at corporateheadquarters via the WAN. Similarly, the sensor computing device 12coupled to LAN 2 collects and processes data regarding the second set ofcomponents and final assembly as sensed by passive wireless sensors 16-3and 16-4. This sensor computing device 12 is able to communicate thisdata to the user computing device 14 coupled to the LAN 2 and/or to thecomputing device 14 at corporate headquarters via the WAN. In such asystem, real time monitor is available locally (e.g., via the LAN) andis further available non-locally (e.g., via the WAN). Note that any ofthe user computing devices 14 may receive data from any of the sensorcomputing devices 12 via a combination of LANs and the WAN.

FIG. 2 is a schematic block diagram of an embodiment of a computingdevice 12 and/or 14 that includes a computing core 20, one or more inputdevices 48 (e.g., keypad, keyboard, touchscreen, voice to text, etc.),one or more audio output devices 50 (e.g., speaker(s), headphone jack,etc.), one or more visual output devices 46 and 52 (e.g., video graphicsdisplay, touchscreen, etc.), one or more universal serial bus (USB)devices, one or more networking devices (e.g., a wireless local areanetwork (WLAN) device 54, a wired LAN device 56, a wireless wide areanetwork (WWAN) device 57 (e.g., a cellular telephone transceiver, awireless data network transceiver, etc.), and/or a wired WAN device 60),one or more memory devices (e.g., a flash memory device 62, one or morehard drives 64, one or more solid state (SS) memory devices 66, and/orcloud memory 68), one or more peripheral devices, and/or a transceiver70.

The computing core 20 includes a video graphics processing unit 28, oneor more processing modules 22, a memory controller 24, main memory 26(e.g., RAM), one or more input/output (I/O) device interface module 36,an input/output (I/O) interface 32, an input/output (I/O) controller 30,a peripheral interface 34, one or more USB interface modules 38, one ormore network interface modules 40, one or more memory interface modules42, and/or one or more peripheral device interface modules 44. Each ofthe interface modules 36-44 includes a combination of hardware (e.g.,connectors, wiring, etc.) and operational instructions stored on memory(e.g., driver software) that is executed by the processing module 22and/or a processing circuit within the respective interface module. Eachof the interface modules couples to one or more components of thecomputing device 12-14. For example, one of the IO device interfacemodules 36 couples to an audio output device 50. As another example, oneof the memory interface modules 42 couples to flash memory 62 andanother one of the memory interface modules 42 couples to cloud memory68 (e.g., an on-line storage system and/or on-line backup system).

The transceiver 70 is coupled to the computing core 20 via a USBinterface module 38, a network interface module 40, a peripheral deviceinterface module 44, or a dedicated interface module (not shown).Regardless of how the transceiver 70 is coupled to the computing core,it functions to communication with the passive wireless sensors.

FIG. 3 is a schematic block diagram of an embodiment of a wirelesssensor 16 that includes an antenna structure 80, a radio frequency (RF)signal circuit 65, a power circuit 55, a processing module 84, memory88, and one or more sensing elements 58. The memory 88 includes one ormore of read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, cachememory, and/or any device that stores digital information.

The sensing element 58 may be a separate device or integrated into theantenna structure. In general, the sensing element 58 functions toaffect the impedance of the antenna structure and/or other operationalcharacteristics of the antenna structure 80 as an environment conditionchanges. For example, the sensing element senses moisture (e.g., thepresence or absence of moisture, a saturation level of moisture, etc.),pressure, temperature, a gas level (e.g., the presence or absence of aparticular gas, a saturation level of the particular gas, etc.), and/orproximity. One or more of the various patents and patent applications towhich this application claims priority discloses various embodiments ofsensor elements 58.

In an example of operation, the processing module 84 enables the RFsignal circuit 65 to generate an RF signal 75. This may be done in acalibration mode (e.g., upon initial installation of the sensor 16, whena calibration signal is received or generated, etc.) or in a sense mode(e.g., enabled to sense an environmental condition). In the sense mode,the RF signal circuit 65 may be enabled periodically, randomly, or uponcommand from a sensor computing device 12.

In the calibration mode, the sensing element 58 is subjected to a knowncondition (e.g., a known moisture (e.g., dry), a known temperature, aknown pressure, a known gas level for a particular type of gas, etc.).With the RF signal circuit 65 transmitting the RF signal 75, the antennastructure 80 receives it. The sensing element 58, being proximal to theantenna structure 80 or integrated into the antenna structure 80, causesa change of an operating characteristic of the antenna structure 80(e.g., impedance, quality factor, resonance, etc.). The processingmodule 84 generates a first digital value based on the change of theoperating characteristic to represent the known condition. Theprocessing module 84 then writes the first digital value into thememory.

In the sense mode, the sensing element 58 is subjected to an unknowncondition (e.g., an unknown moisture level, an unknown temperature, anunknown pressure, an unknown gas level for a particular type of gas,etc.). With the RF signal circuit 65 transmitting the RF signal 75, theantenna structure 80 receives it. The sensing element 58, being proximalto the antenna structure 80, causes a different change of the operatingcharacteristic of the antenna structure 80. The processing module 84generates a second digital value based on the different change of theoperating characteristic to represent the unknown condition. Theprocessing module 84 then writes the second digital value into thememory. Note that the sense mode may be periodically activated toperiodically record values of the unknown condition.

Whether the sensor 16 is in the calibration mode or the sense mode, thepower circuit 55 needs to provide at least one power supply voltage topower the processing module 84, the RF signal circuit 65, and the memory88. In an embodiment, the power circuit 55 includes an active powersupply circuit (e.g., a battery and a power conversion circuit). Inanother embodiment, the power circuit 55 includes a passive power supplycircuit, which, in turn, includes a power harvesting circuit (e.g.,creates a DC voltage from an AC signal, from solar energy, from anultrasound signal, from movement, and/or a combination thereof) and apower sourcing circuit (e.g., power converter, capacitor, battery, solarcells, and/or any other energy storage device).

FIG. 4 is a schematic block diagram of another embodiment of a wirelesssensor 16 that includes the sensing element 58, the antenna structure80, the RF signal circuit 65, the power circuit 55, the processingmodule 84, the memory 88, a tuning circuit 90, and a real time clock 91.The RF signal circuit 65 includes an oscillator 67 and an antenna 69.The power circuit 55 includes a battery 59 and a power harvestingcircuit 82. The processing module 84 includes a detection circuit 87 anda controller 83. The tuning circuit 90 includes an inductor and avariable capacitance (e.g., a varactor). In an embodiment, a Chameleonintegrated circuit manufactured by the Assignee provides the tuningcircuit 90 and the processing module 84.

In an example of operation, the controller 83 enables the oscillator 67to generate an oscillation (e.g., a sinusoidal signal having a frequencycorresponding to a carrier frequency of RF signals communicated betweenthe sensor 16 and the sensor computing device 12). The antenna 69 (whichmay be a loop antenna, a meandering trace, a dipole antenna, a monopoleantenna, etc.) transmits the sinusoidal signal as the RF signal 75. Theantenna structure 80 (which, in this example, includes a dipole antennaand transmission line) receives the RF signal 75.

The received RF signal 75 is provided to the power harvest circuit 82,which produces a supply voltage (Vdd), a reference voltage (Vss), and amid voltage (Vmid). The magnitude of the supply voltage (Vdd) isreflective of the input power of the received RF signal. When the inputof the sensor 16 (e.g., antenna 80, the tuning circuit 90, and thesensing element 58) is in resonance with the frequency of RF signal, theinput power is maximized. When the input of the sensor 16 is not inresonance, the input power decreases proportionally with how far out ofresonance the input has become.

The detection circuit 87 generates a control signal that adjusts thecapacitance of the tuning circuit 90 (e.g., adjusts the varactor). Thedetection circuit 87 also monitors a power indication 57 (e.g., theinput power, the supply voltage, a supply current, input voltage, etc.)that corresponds to the input power of the RF signal 75 with the currentcapacitance setting of the tuning circuit 90. When the power indication57 is at its maximum (or near maximum), the input of the sensor 16 is inresonance (or very close to in resonance) with the RF signal 75.

The controller 83 receives information from the detection circuit 87regarding the adjusting of the control signal to achieve resonance. Thecontroller 83 generates a digital value corresponding to the adjustingof the control signal to achieve resonance. For instance, if the digitalvalue is an 8-bit binary number, then the digital value will be in therange of 0 to 2⁸. The controller 83 then writes the digital value intothe memory.

With the inclusion of a real time clock 91, which produces a clocksignal 93, the controller 83 is able to time stamp each generation of adigital value. As such, a historical record of monitoring a conditioncan be saved in the memory 88 and subsequently retrieved.

FIG. 5 is a schematic block diagram of an example of a sensor computingdevice 12 communicating with a passive wireless sensor 16 (e.g., any oneof 16-1 through 16-4). The sensor computing device 12 is illustrated ina simplified manner; as such, it shown to include the transceiver 70, anantenna 96, the processing module 22, and the memory (e.g., one or more26 and 62-68). The wireless sensor 16 includes an antenna 80, one ormore sensing elements 58, the RF signal circuit 65, a power harvestingcircuit 82, a power detection circuit 86, the processing module 84,memory 88, the tuning circuit 90, a receiver section 92, and atransmitter section 94.

In an example, the sensing element 58 of the wireless sensor 16 sensesan environmental condition of an object. The environment conditionincludes, but is not limited to, one or more of moisture, temperature,pressure, humidity, altitude, sonic wave (e.g., sound), human contact,surface conditions, tracking, location, etc. The object includes one ormore of, but is not limited to, a box, a personal item (e.g., clothes,diapers, etc.), a pet, an automobile component, an article ofmanufacture, an item in transit, etc. The sensing element 58 senses theenvironmental condition (e.g., moisture) and, as a result of the sensedcondition, the sensing element 58 affects an operational parameter(e.g., input impedance, quality factor, frequency, etc.) of an RF frontend of the wireless sensor. Note that the RF front end includes one ormore of the antenna 80, the tuning circuit 90, the transmitter section94, the receiver section 92.

As a specific example, the sensing element 58, as a result of the sensedenvironmental condition, affects the input impedance of the antennastructure 80 and/or of the tuning circuit 90 (e.g., a tank circuit thatincludes a varactor and one or inductors having a resonant frequency,when tune, that corresponds to the carrier frequency of the second RFsignal 85). In response to the impedance change, the processing module84 adjusts the resonant frequency of the tuning circuit 90 to compensatefor the change in input impedance caused by the sensed environmentalcondition. The amount of adjustment is reflective of the level of theenvironmental condition (e.g., a little change corresponds to a littlemoisture; a large change corresponds to a large amount of moisture). Theprocessing module 84 generates a coded value to represent the amount ofadjustment and conveys the coded value to the sensor computing device 12via the transmitter section 94 and the antenna 80 using back-scatteringor other communication protocol.

In addition to processing the sensed environmental condition, theprocessing module 84 processes a power level adjustment. For example,the power detection circuit 86 detects a power level of the received RFsignal. In one embodiment, the processing module interprets the powerlevel and communicates with the sensor computing device 12 to adjust thepower level of the RF signal 85 transmitted by the computing device 12to a desired level (e.g., optimal for accuracy in detecting theenvironmental condition). In another embodiment, the processing module84 includes the received power level data with the environmental senseddata it sends to the sensor computing device 12 so that the computingdevice can factor the power level into the determination of theenvironmental condition.

In communication, the sensor computing device 12 transmits a second RFsignal 85 to the sensor 16. The second RF signal 85 includes acontinuous wave signal that is modulated (e.g., amplitude shift keying)to send the sensor 16 a message. The sensor 16 extracts the message fromthe second RF signal, which, for example, may be a request to send thecollected data to the sensor computing device 12. In response, thesensor retrieves the digital values and corresponding time stamps fromthe memory and sends them to the sensor computing device 12 via thetransmitter.

FIG. 6 is a logic diagram of an embodiment of a method of sensing by awireless sensor that begins at step 100 where the sensor determineswhether it is in a calibration mode or a sense mode. For example, thesensor 16 may receive a signal from the sensor computing device 12 toindicate the calibration mode or the sense mode. As another example, thesensor 16 is powered up in the calibration mode and, after performing acalibration, changes to the sense mode.

When the sensor is in the calibration mode (e.g., sensing a knowncondition), the method continues to step 102 wherein the RF signalcircuit is enabled to generate the RF signal. The method continues atstep 104 where the processing module adjusts the tuning circuit toobtain a resonance of the front end of the sensor at the frequency ofthe RF signal. With reference to the frequency plots on the right of thefigure, the first frequency plot is of the front end prior to adjustingthe tuning circuit and the one on the right is after adjustment.

The method continues at step 106 where the amount of tuning of thetuning circuit is determined. The method continues at step 108 where adigital value is generated based on the amount of tuning. The methodcontinues at step 110 where the digital value is time stamped using aclock generated by a real time clock circuit. The method continues atstep 112 where the time stamped digital value is stored in memory.

When the sensor is in the sense mode (e.g., sensing an unknowncondition), the method continues at step 114 where the sensor determineswhether to enable the RF signal circuit (e.g., has a periodic intervalexpired). If not, the method waits until it is time to enable the RFsignal circuit. When the RF signal circuit is enabled, the methodcontinues at step 116 where the tuning circuit is adjusted to obtain aresonance of the front end of the sensor at the frequency of the RFsignal.

The method continues at step 118 where the amount of tuning of thetuning circuit is determined. The method continues at step 120 where adigital value is generated based on the amount of tuning. The methodcontinues at step 122 where the digital value is time stamped using aclock generated by a real time clock circuit. The method continues atstep 124 where the time stamped digital value is stored in memory.

The method continues at step 126 where the sensor determines whether itis receiving a second RF signal that includes a message requestingretrieval of stored data. If not, the method returns to step 100. If itis receiving the second RF signal, the method continues at step 128where the sensor retrieves the digital values stored in the memory. Themethod continues at step 130 where the sensor sends, via thetransmitter, the retrieved digital values to a sensor computing device12.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

While the transistors in the above described figure(s) is/are shown asfield effect transistors (FETs), as one of ordinary skill in the artwill appreciate, the transistors may be implemented using any type oftransistor structure including, but not limited to, bipolar, metal oxidesemiconductor field effect transistors (MOSFET), N-well transistors,P-well transistors, enhancement mode, depletion mode, and zero voltagethreshold (VT) transistors.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A radio frequency identification (RFID) tagcomprises: an antenna structure operable to receive a radio frequency(RF) signal, wherein the antenna structure includes a sensing element,an antenna, and a tuning circuit, and wherein exposure to anenvironmental condition causes a change in input impedance of theantenna structure while receiving the RF signal, and wherein a desiredinput power level occurs when the antenna structure is in resonance withthe RF signal; a memory; and a processing module operably coupled to theantenna structure and the memory, wherein the processing module isoperable to: measure a first input power level from the RF signal; whenthe first input power level is less than the desired input power level:adjust the input impedance of the antenna structure to increase thefirst input power level; measure a second input power level from the RFsignal at the adjusted input impedance; and when the second input powerlevel substantially matches the desired input power level: determine apower difference between the first input power level and the secondinput power level; generate a digital value based on the powerdifference; and store the digital value in the memory.
 2. The RFID tagof claim 1, wherein the tuning circuit comprises: a capacitor; and avariable inductor, wherein the processing module is operable to adjustthe variable inductor to adjust the input impedance.
 3. The RFID tag ofclaim 1, wherein the tuning circuit comprises: an inductor; and avariable capacitor, wherein the processing module is operable to adjustthe variable capacitor to adjust the input impedance.
 4. The RFID tag ofclaim 1, wherein the processing module is further operable to adjust theinput impedance by: setting the input impedance to an initial impedance.5. The RFID tag of claim 1, wherein the processing module is furtheroperable to adjust the input impedance by: determining an adjustmentbased on a difference between a current measured power level and apreviously measured power level.
 6. The RFID tag of claim 1, wherein theprocessing module is further operable to adjust the input impedance inresponse to an RFID reader command.
 7. The RFID tag of claim 1, whereinthe processing module is further operable to adjust the input impedanceby: using a measurement of the first input power level to adjust theinput impedance.
 8. A method for execution by a radio frequencyidentification (RFID) tag, the method comprises: measuring, by aprocessing module of the RFID tag, a first input power level from areceived RF signal, wherein an antenna structure of the RFID tagincludes a tuning circuit, an antenna, and a sensing element, whereinexposure to an environmental condition causes a change in inputimpedance of the antenna structure while receiving the RF signal, andwherein a desired input power level occurs when the antenna structure isin resonance with the RF signal; and when the first power level is lessthan the desired input power level: adjusting, by the processing module,the input impedance of the antenna structure to increase the first inputpower level; measuring, by the processing module, a second input powerlevel from the received RF signal at the adjusted input impedance; andwhen the second input power level substantially matches the desiredinput power level: determining, by the processing module, a powerdifference between the first input power level and the second inputpower level; generating, by the processing module, a digital value basedon the power difference; and storing, by the processing module, thedigital value in memory of the RFID tag.
 9. The method of claim 8,wherein the adjusting the input impedance includes: setting, by theprocessing module, the input impedance to an initial impedance.
 10. Themethod of claim 8, wherein the adjusting the input impedance includes:determining, by the processing module, an adjustment based on adifference between a current measured power level and a previouslymeasured power level.
 11. The method of claim 8, wherein the adjustingthe input impedance includes: using, by the processing module, ameasurement of the first input power level to determine the adjusting ofthe input impedance.